Q: hangs iphone4 hags up  during calls

Hello asif_pia,

Thanks for using the Apple Support Communities!

From your post, it sounds like you are experiencing dropped calls on your iPhone. To begin troubleshooting this situation, I would suggest working through the suggested steps located in the following article. 

If you can't connect to a cellular network or cellular data - Apple Support

The next article may provide useful information to you as well. 

iPhone 4: Antenna or reception issues - Apple Support

Have a great day!